A 6 in the title would indicate that too, if they called it the 6 people would as for it. Please note, I'm not suggestion "iPhone 6". Marketing would be better to have a 6, it's the 6th revision! "It's the 2012 model, it doesn't matter if we changed it, it's the new model."
With your logic marketing would have been better to called last years a 5.
And the second iPhone had a 3 (3g) in the title (and then a 3gs).
Again, the iPad 3 would have made sense with marketing too. But that's not what they did.
People having the (6th) iPhone 5 running iOS 6 is a support (marketing?) nightmare too. Maybe not nightmare but clearly confusion. People cant keep straight Windows and Office versions ("I've got Windows 2003" or better yet "I've got Microsoft 2000").
Gary
I think you're applying too much "logic" for the average high street consumer, they won't know/care what literal model iteration they're holding (and Apple doesn't want/need them to).
All Apple need you to know (so you can tell others and do their marketing for them), is that it's the latest iPhone.
Mathematical versions are not important to Apple, it just comes down to keeping it simple for their customers.
Here's something I posted earlier:
Isn't the naming convention like a car?
A BMW 3 series for example, has various incarnations, so does the iPhone.
So we've had:
iPhone.
iPhone 3G (3 Series).
iPhone 3GS (still the 3 series).
iPhone 4 (4 Series).
iPhone 4S (still the 4 series).
And now the iPhone 5 (5 series).
It's a series range, not a specific model number relating to which specific version it is mathematically.